<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>
<body>
    <script>
        var arr = []
        arr[0] = '白起'
        arr[1] = '廉颇'
        arr[2] = '吕布'
        arr[3] = '貂蝉'
        console.log(arr);
        arr[arr.length] = '张飞' //arr.length 是名为arr这个数组的长度
        console.log(arr);
    </script>
</body>
</html>